An internal combustion engine requires heat rejection generally either by air or liquid. In conventional vehicles, liquid cooled engines are most common. Liquid engine cooling is accomplished by an engine-driven coolant pump (commonly referred to as a water pump) mounted on the engine block and operated directly by the engine. The pump forces coolant through passages in the engine, where the coolant absorbs engine heat, then the coolant passes through a radiator where heat is rejected, and finally coolant is returned to the pump inlet to complete the fluid circuit. A fan, driven either directly from the engine or by an electric motor, is used in many cases to draw ambient air across the radiator so that heat is rejected at the radiator by transferring heat from the coolant to the ambient air, thus cooling the engine.
A conventional thermostat controls the flow of pumped coolant through the radiator in relation to coolant temperature. The thermostat controls flow through the radiator until the coolant reaches a sufficiently hot temperature to cause the thermostat to allow flow through the radiator such that the radiator may effectively limit engine temperature. In this way, the thermostat performs a form of coolant temperature regulation that establishes a desired operating temperature for the engine once the engine has fully warmed up while inherently allowing the coolant to heat more rapidly when the engine is started from a cooler condition.
Although the above described cooling system is effective in operation, to improve fuel economy, it is preferable to operate the cooling fan and water pump motor based on cooling requirements, rather than on the r.p.m. of the engine.
A need exists to provide a total cooling system incorporating at least one electric coolant pump-motor and an electric fan motor which operate independent of engine r.p.m. and wherein cooling is optimized based on current draw of the coolant pump-motor.